Traditional power steering mechanisms use hydraulic systems to provide their energy. Unfortunately, hydraulic systems must be constantly powered to function properly, placing a drain on an automobile's power system and lowering its fuel efficiency. Additionally, hydraulic steering systems are generally isolated and do not provide steering wheel position information to other systems in an automobile.
Steering wheel position information can be used to adjust an automobile's suspension system, dampening the automobile's shock absorbers to provide a smoother ride, along with compensating for body pitching and yawing due to turns, acceleration or deceleration. To perform these functions, steering wheel position sensors that give advanced input to the controller for anticipatory responses are necessary. Currently available sensors have several drawbacks including their lack of resolution, accuracy, response time, and durability. Also, their large size and high cost of manufacture limit their use in today's automobiles. There have been some recent inventions attempting to overcome these limitations.
U.S. Pat. Nos. 4,420,754 and 4,879,508 to Adermo discuss a capacitive type measurement apparatus for making absolute measurements of position. These patents define a large and continuous array of transmitter electrodes and receiver electrodes from which a ratio of relationships to both the amount of travel and the energizing wave fundamentals provides a signal relative to the position of travel. The systems disclosed in these patents read a fixed series of points as movement takes place. From a select group of these points a number of differing wavelengths are received for measurement. The signals received are then deciphered to determine the position being read. The deciphering electronics are rather complicated and require a significant number of logic and amplifier elements as well as a microprocessor.
U.S. Pat. No. 4,697,144 to Howbrook discloses a position sensor that uses an array of coils with differing phase shifts applied to them. There is a pickup that receives the signals from one or more of these fixed and defined points dependent of the position and resolves the position from the signals received. The sensor coils are used for an inductive stepped measurement system.
U.S. Pat. Nos. 5,955,881 to White et al., U.S. Pat. No. 6,057,682 to McCurley et al. U.S. Pat. No. 5,198,763 to Konishi, U.S. Pat. No. 5,142,225 to Gerlach, U.S. Pat. No. 5,789,915 to Ingraham and U.S. Pat. No. 5,365,791 to Padula disclose a linear measurement system that uses one or more magnets and one or more Hall element sensors to provide a non-contacting position sensor, using magnetic flux and the coupling of such, as the varying property with which sensing occurs. These patents also describe rotary sensors using this technique.
U.S. Pat. No. 6,118,283 to Cripe discloses a capacitive rotary position sensor in which quadrate signals are coupled by position to produce a phase variance to be compared to a reference signal to produce an analog output representation of the rotary position.